1. Field of the Invention
This invention relates to a high-pressure metallic pipe provided with a connecting head part and formed of a steel pipe of a relatively small diameter and a thick wall, frequently used as a conduit for the supply of a fuel in a diesel internal combustion engine like a high-pressure fuel injection pipe measuring approximately 4 to 20 mm in outside diameter and 1 to 8 mm in wall thickness and to a method for the formation of the connecting head part.
2. Description of the Prior Art
The conventional high-pressure metallic pipe provided with a connecting head part is illustrated in FIG. 10 or FIG. 11. The connecting head part (12) is of the shape of a truncated cone having as its seat surface (13) the outer peripheral surface at the terminal part of a thick-wall steel pipe (11). The connecting head part is shaped by a buckling work by the use of the pressure exerted externally by a punch member in the direction of the axis. In consequence of the buckling work due to the aforementioned pressure, the peripheral wall of the connecting head part is expanded outwardly, with the result that an annular pocket (15) (FIG. 10) or an annular notch (15') (FIG. 11) is formed on the inside of the head part. The metallic pipe thus configured is then put to use. The reference numeral (14) stands for a sleeve washer which is fitted behind the connecting head part (12).
The conventional high-pressure metallic pipe provided with a connecting head part and the method for the formation of this connecting head part, however, have entailed the problem that the annular pocket (15) or annular notch (15') inevitably formed inside the connecting head part causes a high-pressure fluid being forwarded through the pipe to induce the phenomenon of cavitation erosion in the pocket or notch and its vicinity.